Cardiac arrhythmias involve an abnormality in the electrical conduction of the heart and are a leading cause of stroke, heart disease, and sudden cardiac death. Treatment options for patients with arrhythmia include medications, such as beta blockers, implantable devices, such as an implantable cardioverter-defibrillator (ICD), and catheter ablation of cardiac tissue.
Arrhythmias can be studied and diagnosed by “electrically mapping” the heart with catheters that are inserted through the patient's vasculature into a heart chamber. Cardiac endocardial mapping is a medical procedure by which electrograms, recorded directly from inside the heart chamber are used to characterize the heart conduction abnormalities. Generally, a mapping catheter can be inserted into the heart and used to map the electrical activity of the heart. The mapping catheter can be used to diagnose and/or treat heart disease. For example, maps can be used identify the origins of an arrhythmia to guide therapies, such as ablation, to treat the arrhythmia.
Contact mapping refers to an approach in which the electrodes are in direct contact with the heart wall. Electrodes are utilized for recording electrograms at different positions on the wall of a heart chamber, such as an atrium, so that various and important electrophysiological variables can be measured and analyzed from the electrogram recordings. Such variables include voltage potential, local activation times, fractionated voltage potentials, potential distribution during depolarization and repolarization, and vectorized data including conduction velocity and direction. Cardiac mapping is very important in locating aberrant conduction sites in the heart and the mapping catheter is frequently utilized to guide ablation. Various types of contact catheters have been developed that include catheters that are somewhat large and are designed to fill the entire heart chamber, or are smaller and need to be moved within the heart chamber to sequentially map various areas of the heart.
Endocardial mapping catheters have been of limited capability because they only have a few electrodes which makes it difficult to accurately map the heart. The most commonly used mapping catheters have multiple electrodes arranged along a single axis, typically ring electrodes encircling the catheter shaft at or near the distal end of the catheter, the portion of the device inside the heart.
In order to obtain a full chamber map it has been necessary to maneuver the distal extremity of the catheter extensively and to reposition it incrementally over the entire chamber of the heart. Such a procedure has been found to be time consuming and relatively inaccurate. Webster (U.S. Pat. No. 4,960,134) describes a symmetrical cylindrical control handle to enable accurate and precise catheter tip section movement. However, this improvement does not eliminate the need to maneuver across the endocardial surface to map a heart chamber. This method, called sequential contact mapping, does not provide a whole chamber map during a single cardiac cycle. In addition, a user must hold the catheter in position, often with his hand positioned awkwardly, making it difficult and inconvenient for a single operator to use separate mapping and ablation catheters. Ideally, the operator would be able to leave a mapping catheter in place without the need to position it with his hands so he/she can concentrate on maneuvering and positioning the ablation catheter. Ablation catheters have mapping capability, however, they only offer a few electrodes severely limiting their mapping utility.
Various attempts have been made over the years to provide arrays to map the cardiac walls. However, the use of undersized arrays of electrodes necessitates maneuvering the catheter in stepwise fashion across the entire endocardial wall, stopping at each increment to measure electrograms, then proceeding to the adjacent unmapped region until the whole chamber has been mapped in this manner. This method using an array of electrodes is called regional sequential mapping. It is not possible to create a whole chamber map in a single beat of the heart using this design. The regional mapping approach is time consuming. Moreover, in unstable arrhythmias such as atrial fibrillation, this design is inadequate to guide ablation.
Mapping catheter usually requires a sophisticated steering system to position and maneuver the catheter within the patient's vasculature and heart chamber, adding complexity and cost. Additionally, the steering apparatus is sometimes located within the lumen of the catheter thereby obstructing the lumen from other uses. Moreover, the operator will likely need to hold the mapping catheter in position to guide ablation, making it difficult for a single operator to map and ablate using two different devices. Thus, there remains an unmet need to provide a mapping catheter that increases electrode count, reduces complexity and cost, and provides for an instantaneous whole chamber map. Such a device should ideally be stable when positioned in the heart chamber to enable an operator to easily and quickly ablate tissue with a separate catheter.
As medical knowledge increases, catheterizations have become more complicated and more exacting. Today, most catheter ablation procedures are to treat atrial fibrillation. Most catheters used today were developed to treat simpler focal arrhythmias that tend to be very stable. However, when ablating atrial fibrillation or other complex macro-arrhythmias such as atrial flutter, these devices have significant limitations that result in long procedure times, poor outcomes, and an unacceptably high rate of complications.
Moreover, electrical abnormalities are usually diagnosed by mapping electrical activation paths along the endocardial surfaces of the heart chambers over time. The medical professional may place several catheters within one or more chambers of the heart to construct a map of sufficient detail to make an accurate diagnosis and to help determine ablation sites as part of a treatment strategy. Sometimes this electrical activity is cyclical, meaning it repeats beat after beat. In such cases, a simple mapping catheter with a linear set of electrodes may serve to perform the diagnosis by moving the catheter distal section to various regions and then point-by-point comparing activation times with a reference. The stability of the arrhythmia allows for this somewhat cumbersome technique. However, certain types of electrical activity within a heart chamber are not cyclical. Examples include atrial fibrillation. Such electrical activity is random. To analyze or map this type of electrical activity, all the points of the map must be obtained simultaneously. Moreover, since the chaotic nature of fibrillation has consequent effects throughout the chamber with respect to out-of-rhythm depolarizations, a view of the entire heart chamber is also beneficial.
Most mapping catheters utilize multiple components fabricated into discrete multi-electrode assemblies that can limit the number of electrodes that can practically be incorporated into the catheter. Each wire assembly adds unwanted stiffness to the catheter and the individual components can only be reduced in size to practical limits dictated by several factors such as assembly, machining capabilities, and strength requirements. Assembling individual components into a subassembly as described requires labor-intensive processes escalating the cost to manufacture such a device.
Another approach considered in the manufacture of mapping catheters is the use of flexible circuits, also known as “flex circuits.” They consist of a thin insulating polymer film having conductive circuit patterns affixed thereto and typically supplied with a thin polymer coating to protect the conductor circuits. Polyimide is a common substrate material for a flex circuit but is typically thick imparting unwanted stiffness and poor resilience when used in a catheter. Also, when a flex circuit was used, it was often prone to kinking in the small curvatures required of an expandable array. Most, importantly, however, was that it was impractically expensive to form flex circuits of sufficient length to use in a catheter. Soldering individual wires to a flex circuit within the length of the catheter made for complicated and expensive manufacturing techniques. Multiple interconnections of flex circuits to other flex circuits or other components can increase the noise level along the circuit path, which can decrease the flex circuit's usefulness for detecting very low level electrical cardiac signals. While flex circuits have yielded some improvements in the circuitry field, flex circuit technology, while suggestive of potential, does not improve upon existing mapping catheter designs.
After the mapping catheter and associated system have identified the anatomic origin of the aberrant electrical conduction in the wall of the heart chamber, the medical professional may then proceed to ablate the offending tissue, thus treating the arrhythmia. Catheter ablation procedures have evolved in recent years to become an established treatment for patients with a variety of supraventricular and ventricular arrhythmias. The typical catheter ablation procedure usually utilizes targeted ablation of the site with an ablation device such as, but not limited to, a radio frequency (RF) catheter, that delivers a burst of high energy which affects the heart tissue by scarring the tissue to terminate the tissue's ability to allow natural electrical pulses to pass through aberrant conduction pathways. This procedure usually takes place in an electrophysiology laboratory and may last for several hours most of which is spent mapping the electrical conduction in the heart.
Although contact mapping catheters and systems are known in the art, there is a continuing need to improve the accuracy, stability, and maneuverability of such devices and systems so that they can be more widely used, especially as an adjunct to cardiac ablation procedures.
A need has also been recognized for an endocardial mapping catheter that incorporates a large number of electrodes making it possible to perform endocardial mapping accurately and rapidly and at a higher resolution, and that make possible simultaneous measurements of an entire chamber in the heart by providing electrode coverage over the entire area.
A further need has been recognized for a high electrode count within a shaft diameter compatible with typically used 8.5Fr trans septal delivery sheaths. Another need is for the ability to adapt the electrode carrying element, the splines, to conform to the heart chamber so the electrodes come into intimate contact with the heart wall while accommodating the wall motion of a beating heart.
Yet another need in the field is to be able to configure bipolar electrode pairs of sufficiently close spacing to precisely map areas of ischemia, where voltage potentials are low, areas of Complex Fractionated Atrial Electrograms (CFAE), and other anomalous regions with aberrant conduction patterns.
A still further recognized continuing need is to provide a system and method of the above character in which the electrodes are expanded into engagement with the wall of the chamber of the heart and are maintained in engagement with that wall during pumping action of the heart.
Still another need is for a system and method in which the electrodes are conformably retained in engagement with the wall forming the chamber of the heart during the time that the heart is expanding and contracting the chamber.
More needs include a device in which the presence of the distal extremity of the device; i.e., the mapping basket, in the heart does not substantially impede the flow of blood in the chamber of the heart. Additionally there is a need for a system and method of the above character in which the mapping and ablation procedures can be carried out without movement of the distal extremity of the catheter with respect to the wall forming the chamber of the heart.
And yet further needs exist for sufficient space between the splines of the basket to enable easy manipulation and positioning of an ablation catheter, and for a cost effective and densely packed interconnect method to route a large number of isolated electrical signal lines through a mapping catheter of a size accepted for use in these procedures. The invention fulfills these needs and others.